1. Field of the Invention.
This invention relates to improvements in apparatus for seismic exploration, and more particularly to improvements in apparatus for generating seismic waves.
2. Description of the Prior Art
The invention preferably employs a seismic wave generator of the gas exploder type described in U.S. Pat. No. 3,958,661 to Dransfield. In this patent an elongated upstanding cylindrical housing contains a movable piston element disposed above an expansible combustion chamber and below a downwardly biasing gas compression chamber. Ignition of a combustible gas mixture in the combustion chamber drives the housing downwardly to impart a seismic pulse to the earth and drives the piston upwardly in reaction. The housing is then drawn upwardly responsive to the increasing pressure within the compression chamber and to the reaction of the earth itself. A prior art apparatus for carrying such a generator is disclosed in U.S. Pat. No. 3,810,524 to Dransfield. According to this patent, the previously described piston is connected to a "catcher" which, upon firing of the device, controls the movement of the generator until it returns to an initial rest position. The upward recoil of the generator is guided by means of roller, gear type, or sliding contact between a piston rod extending upwardly from the piston and an external framework. The piston rod also interconnects the generator, by means of a yoke, with the dashpot pistons of a pair of fixed fluid-filled dashpot cylinders. After the generator reaches its maximum height, these cylinders return it slowly to its initial firing position.
As emphasized in the above-referenced patents, a lightweight seismic gas exploder of elongated tubular construction possesses significantly advantages. Truck transport is simplified and deployment is facilitated particularly in muddy or marshy environments. However, it is apparent that the external framework described above by means of which the recoil and return of such a generator is guided and controlled takes up considerable space in addition to that occupied by the generator itself, whether freestanding or truck mounted. Therefore, to enhance the maneuverability of the device, the present invention eliminates this framework, while at the same time preserving the elongated shape and silhouette of the generator.
It is conventional to perform the damping functions of the dual hydraulic cylinders discussed above by means of a single, upstanding cylinder mounted directly above and interconnected with the movable piston of a seismic gas exploder. The invention to be described utilizes such a combination in an apparatus designed to meet the objectives set forth herein.